Most loudspeakers consist of a transducer unit, often called xe2x80x9cdriver,xe2x80x9d and an enclosure of some sort. Many different forms of loudspeaker enclosures are known.
Loudspeaker drivers convert electric signals into sound. The quality of the sound output from a loudspeaker system depends not only on the quality of the driver unit itself, but also on the quality and the design of the enclosure. The combination of the characteristics of the loudspeaker driver and its enclosure may determine the overall performance and sonic signature of the loudspeaker system.
Loudspeaker drivers are often bipolar transducers, in that they produce sound both from both their front and rear. The sound fields produced at these opposite ends of the driver are out of phase and combine destructively reducing output in the low frequency domain of the audible range.
One class of loudspeaker enclosures uses acoustic waveguides to process the output from the rear of the driver and reverse its phase, resulting in constructive interference, which enhances the output of the system in the low frequency domain. These enclosures are known as transmission lines. Transmission lines presently used have tubes with constant or linearly tapering cross sections, with the driver mounted at the end with the larger cross section. Disadvantages of this approach include the fact that the waveguide only reverses the phase of certain frequencies that are related to the acoustic length of the transmission line. This causes destructive interference to occur at the frequencies whose phase is not reversed, producing sound output that is not constant with the frequency of the reproduced sound.
Horn loudspeakers are also known. A horn loudspeaker has a tapering tubular waveguide with the driver mounted at the end of smaller cross section, and an enclosure at the rear of the driver. The horn acts as a high pass filter/amplifier, thereby enhancing the output of the driver above a certain frequency. Size limitations often limit horn sizes in practice for mid-high frequency domain of the audible spectrum.
The present application describes a transmission line loudspeaker, which uses a non-linearly tapering acoustic waveguide.
In specific embodiments that are disclosed herein, the non-linearly tapering transmission lines may preserve the benefits of the conventional transmission line designs. In addition, non-linearly tapering transmission lines act as low pass filters, thereby attenuating the high frequency components of the sound produced at the rear of the driver which, in a conventional transmission line, would combine destructively with the high frequency components of the sound radiated at the front of the driver. This results in smoother overall frequency response of the loudspeaker system. Non-linearly transmission lines also permit a greater amount of impedance matching between the driver and the waveguide, resulting in improved transient response, reduced distortion, and a smoother and less dramatic decay in sound output below the resonant frequency of the system.
The driver may be placed at the largest opening of the transmission line, and a transmission line is caused to nonlinearly taper towards its terminus or output. The transmission line may be folded over itself to increase its length.